Are you planning to take the MCAT this year? If so, you should take a careful look at the preparation materials available from the AAMC, the organization that produces the exam. These materials include the very first book that you should read about the exam, The Official Guide to the MCAT, an exceptionally useful volume that includes information about the medical school application process as well as information about the test itself. Other AAMC materials include online practice tests that are based on real MCAT items; students tell me that the scores they earn on the practice tests are reasonably good predictors of the scores that they earn when they take the actual MCAT.
Now, the AAMC has produced a useful package of self-assessment tools that will help you identify your strengths and weaknesses at the beginning of the MCAT preparation process. It includes hundreds of real MCAT questions. You can buy a full package that includes questions for each of the subtests, or buy materials for the subtests that most interest you individually. You can even buy a discounted package that includes the self-assessment materials, a practice test, and The Official Guide to the MCAT. See www.aamc.org/mcatsap for all of the details.